Image perspective error has long been recognized in the photographic arts. Traditionally, image perspective correction has been accomplished using view cameras or shift lenses. For some time now, bellows-type view cameras have been used to tailor the perspective and depth of field to the individual scene desired to be photographed. In many cases, bellows-type view cameras can provide photographs not possible with rigid cameras; that is, cameras with a fixed relationship between the lens and the image plane. As is known in the camera arts, bellows-type view cameras have the capability to raise and lower a lens plane relative to the image plane and vice-versa. In addition, the lens plane and/or the image plane can be tilted.
In operation, translating the image plane or the lens plane changes the field of view while maintaining constant depth of field. Tilting the lens plane or the image plane alters the orientation and shape of the depth of field volume, but does not affect the field of view. Lens movements do not affect perspective, but require high lens coverage to avoid image transitions near the borders of captured images. In contrast, image plane movements affect perspective, but do not require high lens coverage.
Although bellows-type view cameras control perspective and depth of field, they are cumbersome, expensive, and generally used only by professional photographers. Attempts have been made to provide some of these control features in rigid cameras. One solution is to add what are known as perspective control lenses or shift lenses. Shift lenses provide large coverage and built-in translational adjustments. However, shift lenses are expensive and have inferior features relative to conventional lenses. For example, shift lenses have fixed focal lengths and manual aperture adjustments. Another solution has been to provide lenses for rigid cameras with both translation and tilt capabilities. However, these lenses are extremely expensive and the tilt feature is in one direction only.
Still other solutions include repositioning the camera with respect to the subject-of-interest. One solution would be to position the camera such that the camera is half as high as the height of the subject-of-interest. This solution still requires that the camera be positioned a specific distance from the subject-of-interest to achieve correct perspective. A second repositioning solution requires a clear distance between a level camera and the subject-of-interest to achieve correct perspective in an image. This solution is not always possible and creates an image where the subject-of-interest fills only a portion of the available image plane. For example, it is often impossible to find a location with a clear view of a tall building where a level camera can capture the entire building.
Digital image-capture devices are configured to capture images that are stored in a memory device or on a suitable storage medium as digital information. The orientation of the captured image initially corresponds to the orientation of the image sensor, such as a charge-coupled device (CCD) or the like, because the image sensor is physically fixed in position within the digital image-capture device. When the digital image-capture device is held by the user in an “upright” position, such that the top portion of the CCD corresponds to the top portion of the image to be captured, the captured image, when viewed on a display, will be properly oriented on the display. That is, the top of the captured image will be displayed at the top of the display. However, the user of the digital image-capture device may on occasion choose to capture the image when the digital-image capture device is oriented in a “non-upright” position. It is often the case that the user of the digital image-capture device will not arrange the image sensor such that it is substantially parallel with a longitudinal axis of relatively tall subjects-of-interest.
Some digital image-capture devices have systems for recording orientation information associated with the capture of still images, for example U.S. Pat. No. 6,563,535, Image Processing System For High Performance Digital Imaging Devices; U.S. Pat. No. 5,764,535, Image Authentication Patterning; U.S. Pat. No. 6,532,039, System and Method For Digital Image Stamping; U.S. Pat. No. 6,275,269, Positioning Stamps In Images Captured With An Image Capture Unit; U.S. Pat. No. 6,011,585, Apparatus And Method For Rotating The Display Orientation Of A Captured Image; and U.S. Pat. No. 6,476,863, Image Transformation Means Including User Interface. While orientation sensors could provide the necessary information to correct perspective errors, it is not always cost effective or desirable to add orientation sensors to digital image-capture devices.
Therefore, it is desirable to introduce low-cost systems and methods for perspective correction in captured images without need for orientation sensors, additional lenses, and lens adjustments.